The present invention relates to a multiplex transmission system using a CSMA/CD (Carrier Sense Multiple Access/Collision Detection) transmission system.
There has been proposed a multiplex transmission system using a CSMA/CD transmission system, wherein a plurality of nodes are coupled together through a transmission path, data is transmitted frame by frame from any one of the nodes as a transmission node, and when the data is received properly, the reception node returns a reception acknowledgment signal to the transmission node upon reception of the frame.
FIG. 1 schematically shows the structure of a multiplex transmission system for vehicles which uses the CSMA/CD transmission system. As illustrated, a plurality of nodes comprising, for example, a front multiplex node FN, a combination switch node CS, a meter node MT, and a rear multiplex node RN, are coupled together through a multiplex transmission path (bus) MB composed, for example, of a twist pair type electric wire.
The front multiplex node FN is coupled to a front turn-right signal lamp 6, a front turn-left signal lamp 7, a front small lamp 8, and a horn 9. The combination switch node CS is coupled to a turn-right switch 10, a turn-left switch 11, a small lamp switch 12, a horn switch 13, and a head-lamp high beam switch 14. The meter node MT is coupled to a turn-right indicator 15, a turn-left indicator 16, and a head-lamp high beam indicator 17. The rear multiplex node RN is coupled to a rear turn-right signal lamp 18, a rear turn-left signal lamp 19, and a tail lamp 20 (which is turned on when the small lamp switch 12 is on).
In this multiplex transmission system for vehicles, vehicle driving information is transmitted for each frame F having the format as shown in FIG. 2.
The frame F includes as SD (Starting Delimiter) code, a destination address (16 bits), a local or source address, a data-length data, data 1 to data N, and a check code.
The SD code is a specific code indicating the start of the frame F. The destination address is designated by the value of a physical area assigned in the destination address field for each node, and not by the value of a physical address (or a real address). More specifically, an address area consisting of a plurality of bits is provided in the frame F to specify the destination address and is divided into a plurality of bit areas, and the divided bit areas are respectively assigned to the addresses of the nodes.
FIG. 3 illustrates an example of frame format including such a destination address field. In this example, each node is assigned with different one bit of the destination address field consisting of 16 bits. The 16 bits are respectively assigned to the nodes from the first bit in the ascending order of physical address of the nodes, and the nodes are designated by setting their respective bits to 1. For instance, to designate the nodes N3 and N5 as the destination, the destination address having its third and fifth bits from the start set to 1 and the remaining bits set to 0, i.e., 0010100000000000, needs to be transmitted. The destination address may not be assigned such that one bit is assigned to each node in the ascending order of physical address of the nodes; however, assigning the bits of the destination address field equally (e.g., 1 bit) in the order of physical address of the nodes serves to minimize the scale of the circuit for realizing the system.
In the local address field is written the address of that node which transmits the frame F, so that reception nodes, upon receiving this frame, can detect from which node the frame has been transmitted. The data length field is written with the number of data following this field; if there are N data, then N is written as indicating the data length. Upon reception of the frame, the reception nodes read the data by the data length. The transmission content of the frame following the data is the check code (error detection code) by means of which the end of the frame can be detected. In order to assure the data transmission, each reception node judges by means of the check code whether or not the contents of the received frame are correct, and if they are correct, the reception node sends its local address onto the transmission path MB as a reception acknowledgment (ACK) signal A.
An ACK field for the ACK signals has its ACK signal return areas assigned to the respective nodes in the same order as the destination address field, for the acknowledgment of proper reception of the frame. More specifically, the ACK signal return areas having the same length as the destination designation areas of the destination address are provided, and the ACK signal specific to each node is returned to the ACK signal return area assigned to this node.
In this example, if both of the nodes N3 and N5 have properly received the frame, the nodes N3 and N5 send 1 to the third and fifth bits of the ACK field, respectively, and the transmission node N1 receives 0010100000000000 as the ACK signals A3 and A5. The node N1, which transmitted the frame F, performs an operation as to whether or not the destination address coincides with the value of the ACK field, in order to judge whether or not the desired frame F has been properly transmitted to the destination. More specifically, when a node transmits the frame F to the destination and then receives the ACK signals from other nodes, it compares the information carried by the ACK signals with the information of the destination address of the frame, to discriminate the success/failure of the signal transmission. The multiplex transmission system described above will be hereinafter referred to as the first prior art system.
Apart from the first prior art system, another system shown in FIGS. 5(a-d), hereinafter referred to as the second prior art system, can also be used. As shown in FIG. 5(a), the frame format is the same in structure as the one shown in FIGS. 2 and 3(a-c). In this case, however, a functionally-given address (function address), not a physical address, is designated as a destination address, and the reception nodes return the ACK signals A as shown in FIGS. 5(b)-5(d) in accordance with this address. The function address mentioned here corresponds to the functional addressing mentioned in the article "A Proposal for a Vehicle Network Protocol Standard" presented in the SAE International Congress and Exposition (Feb. 1986).
In the example of FIG. 4, assuming that the physical addresses of the nodes N1-N5 are 1 to 5, respectively, the function address to be transmitted from the node N1 may be determined as illustrated in the following TABLE 1.
As seen from Table 1, the function address "4" indicates that the nodes N2 and N4 are the destination nodes, while the function address "5" indicates that the nodes N2, N4 and N5 are the destination nodes.
TABLE 1 ______________________________________ Function Physical Address Address 2 3 4 5 ______________________________________ 1 * 2 * 3 * 4 * * 5 * * * 6 * * ______________________________________
In the second prior art system, the individual nodes N1-N5 have their respective correlation tables for transmission use between the function addresses and the physical addresses, as shown in TABLE 1 illustrating an example of the table for the node N1, so as to be able to recognize to which physical nodes to transmit the frame. The individual nodes also have their respective reception function tables for reception use, as shown in TABLE 2 illustrating an example of the table for the node N4, so that it can recognize the frames of which function addresses to receive.
TABLE 2 ______________________________________ Function Address To Be Received By Node N4 ______________________________________ 4 5 8 11 14 . . . ______________________________________
In this example, the first three function addresses ("3," "4" and "5") are to be transmitted from the node N1, and the following three function addresses ("8," "11" and "14") are to be transmitted from the node N2.
Assuming that the data B is to be transmitted from the node N1 to the nodes N3 and N5, it is understood from the function address-physical address correlation table (TABLE 1) that the data can be simultaneously transmitted to the nodes N3 and N5 by setting the function address to "6."
In this manner, the frame F is transmitted from the node N1, as shown in FIGS. 6(a-c). The nodes N3 and N5 recognize that they should receive the frame F, based on their own reception function tables (similar to that shown in TABLE 2 for the node N4).
The nodes N3 and N5 receive the frame F, and then return their local addresses as the ACK signals A to the node N1, as shown in FIGS. 6(b)-6(c), if no data error is detected by means of the check code. In this case, the ACK signals A may simultaneously be returned from a plurality of nodes. This can be solved by designing each of the nodes to have the bit-by-bit collision detection function, the transmission inhibition function from the succeeding bit, as well as the ACK signal re-transmission function. With this design, therefore, upon completion of the frame transmission, the ACK signals from the nodes which have received the frame F are set in the order of strength of the address codes with regard to the transmission path structure.
The node that has transmitted the frame F collates the returned ACK signals with the function address-physical address correlation table for transmission use, such as the one shown in TABLE 1, to detect if the ACK signals are returned from all the nodes which should receive the frame F.
If the ACK signal is not returned from any one of the expected reception nodes, the same frame is re-transmitted.
In multiplex transmission systems for vehicles already known, inclusive of the above-mentioned two systems, in order to determine whether or not any of the multiplex nodes is defective, a "trouble-discrimination request frame" is transmitted regularly from a trouble-discriminating multiplex node to the other multiplex nodes. More specifically, the trouble-discriminating multiplex node transmits the "trouble-discrimination request frame" at regular intervals separately from the transmission of ordinary control data. If all the multiplex nodes return the reception acknowledgment signals, the trouble-discriminating multiplex node judges that all of the multiplex nodes are normal. If the reception acknowledgment signal is not returned from any one of the multiplex nodes, the trouble-discriminating multiplex node judges this node to be defective. Thus, the trouble-discriminating multiplex node serves to check the function of the other nodes.
According to the first prior system, however, a problem arises in that, when those multiplex nodes which are not registered as the destination address are required to receive a frame data due to the change of design, for example, the destination address must be modified each time when necessary. A multiplex transmission system capable of flexibly updating the destination address may be employed. However, if the addresses of the necessary multiplex nodes are deleted from the destination address by mistake, the nodes cannot receive the frame.
Similarly, the second prior art system is disadvantageous in that when the design is changed, the recognition pattern of the function addresses of each of the nodes, shown in TABLES 1 and 2, must be changed.
The multiplex transmission systems for vehicles have different multiplex node structures depending on the model and class or grade of vehicles, due to diverse requirements for the functions to be provided. Furthermore, there are three states in respect of power supply in ordinary vehicles, i.e., a "+B" state wherein power is all the time supplied from the batery even if the engine key is in an off position, an "ACC" state wherein power is supplied when the engine key is in an "accessory" position, and an "IG" state wherein power is supplied when the engine key is in an "ignition ON" position. One of these three states of power supply is selected in accordance with the position of the engine key, i.e., the driving condition of the vehicle. Since the multiplex nodes to be supplied with power differ depending on their usage, the operating multiplex node structure of the multiplex transmission system must be changed simultaneously with the changeover among the three states of power supply.
In some cases, a multiplex node may become defective due to some abnormality. In the case of a multiplex transmission system for vehicles which has the re-transmission function mentioned above and in which the data to be compared with the ACK signals (i.e., the destination address in the first prior art system, or the function address-physical address correlation table in the second prior art system) is not changed, it is hard to suitably set the system in accordance with the model and grade of vehicles as well as the power supply states mentioned above. If a multiplex node becomes defective, moreover, the frame must be re-transmitted each time the frame transmission is made, which leads to an increase in transmission amount, i.e., traffic amount.
In order to realize the function addressing of the second prior art system, the multiplex transmission processing circuit of each node is required to have a memory with large capacity for storing both the function address-physical address correlation table for transmission use and the function address table for reception use, and a memory control circuit. This results in an increase in scale of the circuit of the system and in cost.
The conventional trouble discrimination method uses a special message for this purpose only, and therefore, the transmission amount is increased. In addition, the trouble-checking multiplex node, i.e., trouble-discriminating multiplex node, is supplied with the trouble discrimination data from all the other multiplex nodes. Thus, the method has a problem in that if the trouble-discriminating multiplex node itself becomes defective, it will wrongly judge that some nodes are defective, even when the nodes are non-defective, or the trouble discrimination itself cannot be carried out.